1. Field of the Invention
The present invention generally relates to an image formation apparatus such as a plotter, and a multifunction machine capable of at least two functions out of copying, printing, and facsimile operations, and especially relates to an image formation apparatus that reads an image formed under predetermined conditions by an optical reflection type density sensor, wherein image formation conditions are adjusted according to an output value of the density sensor.
2. Description of the Related Art
Recently and continuing, documents are often required to be in colors, and swift processing is required. Accordingly, laser beam printers are made capable of color printing and high-speed printing.
For example, a color electronic photography apparatus of a tandem system for forming a color image is known, wherein toners in yellow (Y), cyan (C), magenta (M), and black (K) colors are used. The apparatus includes image formation units for the colors for forming toner images in the colors, wherein the toner images are superposed on a middle transfer object so that a color image is obtained.
Generally, according to the electronic photography apparatus of the tandem system, the toner images in different colors are independently formed by two or more image formation units one by one on corresponding photo conductors, and the toner images on the photo conductors are superposed on the middle transfer object.
Conventionally, in order to make uniform the density of images, a density patch (test image) is formed on the photo conductor and the middle transfer object under predetermined conditions, an amount of toner adhering (toner adhesion amount) to the density patch is detected by an optical reflection type density sensor, and toner adhesion amount control is performed so that the image formation conditions are adjusted. The image formation conditions include parameters about toner supply to a development unit, electrification potential, development bias potential, and exposure potential.
As disclosed by Patent Reference 1, it is known that the image formation conditions can be more accurately controlled based on the toner adhesion amount of an output image after fixing, rather than based on the toner adhesion amount of the density patch formed on the photo conductor and the middle transfer object.
[Patent Reference 1] JPA 2000-184158
[Patent Reference 2] JPA 2005-077502
[Patent Reference 3] JPA 2004-029217
[Patent Reference 4] JPA H05-333652